25-hour Countdown begins for ISRO’s commercial mission for European Space Agency

Sriharikota, Andhra Pradesh, Dec 3 (PTI) The countdown for ISRO’s dedicated commercial mission, the launch of Proba-3 spacecraft of the European Space Agency (ESA) slated for December 4. began here on Tuesday.

Wednesday’s launch would be a technology demonstration mission. NewSpace India Ltd is the commercial arm of ISRO which would launch client vehicles and has secured the order from the European Space Agency for its latest mission.

“The 25-hour countdown started at 3.08 pm on Tuesday and right now the preparatory works (for the launch) are going on,” an ISRO official told PTI on Tuesday.

Dubbed as the world’s first initiative, the Proba-3 (Project for Onboard Autonomy) consists of a double-satellite in which two spacecraft would fly together as one, maintaining precise formation down to a single millimetre to study the sun’s outer atmosphere.

‘Probas’ is a Latin word, which refers to ‘Let’s try’. The mission objective is to demonstrate precise formation flying and the two spacecraft – ‘Coronagraph’ and ‘Occulter’ would be launched together in a stacked configuration, ISRO said.

The Bengaluru-headquartered ISRO is using its dedicated workhorse Polar Satellite Launch Vehicle (PSLV) for the mission.

The PSLV is on its 61st flight and the 26th of the PSLV-XL variant and it is scheduled for a lift-off from the first launch pad at this spaceport at 4.08 pm on December 4.

The 44.5 metre tall rocket after travelling for about 18 minutes is slated to place the 550kg Proba-3 satellites into a desired orbit.

After reaching the initial orbital conditions, the two satellites would fly 150 metres apart (as one large satellite structure) in tandem so that the ‘Occulter’ spacecraft would block out the solar disk of the sun enabling Coronagraph to study the corona of the Sun or the surrounding atmosphere, for scientific observation.

“The corona-much hotter than the Sun itself, is where space weather originates and a topic of widespread scientific and practical interest,” the ESA said.

The significant objective of the mission is formation flying in precision and to study the Sun’s outer atmosphere.

This pattern of (blocking the solar disk of the sun) formation occurs during solar eclipses and that too for a few minutes for scientists to study. However, the European Space Agency said with Proba-3, the mission would be able to create ‘solar eclipses on demand.’

The two satellites would fly together as a ‘large rigid structure’ in space to prove formation flying technologies and rendezvous experiments, the ESA said.

“The mission will demonstrate formation flying in the context of a large-scale science experiment. The two satellites will together form an approximately 150-metre long solar coronagraph to study the Sun’s faint corona closer to the solar rim than ever before it has been achieved,” it said.

ISRO would be facilitating the launch while European Space Agency scientists would take up study on the mission, post it reaching the desired orbital conditions.

For ISRO, this launch would provide key insights on taking up scientific experiments on the Sun after its maiden mission–Aditya-L1 which was successfully launched in September 2023.

After lifting-off at the scheduled time of 4.08 pm on Wednesday, the satellites are expected to reach high earth orbit and would have a 19.7 hour orbital period with 60,530 km of apogee (farthest point from earth) and 600 km perigee (closest point to earth).

ISRO has used the PSLV-XL variant to carry heavy payloads of about 500 kg in the ambitious Chandrayaan, Mars Orbiter Missions.

The Coronagraph spacecraft in Proba-3 weighs about 310 kg while the Occulter spacecraft is 240 kg.

The Proba-3 mission follows the earth observation satellite Proba-1 launched by ISRO in 2001 and Proba-2 in 2009. The European Space Agency had also launched the Proba-V mission in 2013.

Europe has made significant progress in multi-satellite missions in the past including the ‘Automated Transfer Vehicle’ mission which demonstrated precision down to a few centimetres when docking with the International Space Station.

Sweden’s Prisma Mission also demonstrated formation flying for brief periods, maintaining centimetre level accuracy across tens of metres, the ESA said.